1. Field of the Invention
The present invention relates to optical apparatuses and, more particularly, to optical apparatuses generating line patterns on objects.
2. Description of the Prior Art
Structured light patterns are widely used in 3D profiling systems and machine vision applications. For instance, the generation of a line of light on an object can be used to determine and digitize the shape of an object in 3D profiling systems. Line patterns are also used in helping to recognize and locate an object in an environment in machine vision applications.
The known line generators that are found on the market today use cylindrical optics to expand a light beam, such as a laser beam, in one direction to create a line of light. Lines of light generated by cylindrical optics are qualified as being Gaussian lines of light, and are characterized in that they have a bright center and fading extremities. In other words, the intensity of a Gaussian line of light fades away towards the ends of the line, as illustrated by FIG. 1, wherein x is the length coordinate and I(x) is the longitudinal intensity profile as a function of the length coordinate. The longitudinal line intensity distribution has the highest intensity in the center of the line of light, and the light intensity decreases from the center to the ends of the line of light. The decrease in light intensity the ends of the line is problematic, as the light intensity thereof eventually falls below threshold levels of devices, such as detectors, that detect the line of light, and thus the ends of the line become invisible to these devices. As another example, in 3D profiling systems, because the light intensity of lines is non-uniform, the calibration of charge-coupled devices can also become very difficult. Separate calibrations must be made for pixels in the bright central line portion and for those in the transitional line portions. Low intensity line portions at the ends of the line cannot contribute to the calibration, as they are not visible to the device.
U.S. Pat. No. 4,826,299, issued on May 2, 1989 to Powell, describes optical lenses for projecting a laser beam in a linear pattern that overcomes the limits of the Gaussian linear patterns of cylindrical optics. The lenses of U.S. Pat. No. 4,826,299, also known as Powell lenses, produce an efficient flat-field line pattern (i.e., on a flat surface) and have thereby solved prior problems associated with the Gaussian line projection of laser beams. The intensity distribution of the flat-field line pattern resulting from the use of a Powell lens is illustrated in FIG. 2, wherein x is the length coordinate and I(x) is the longitudinal intensity profile as a function of the length coordinate. The flat-field line pattern provides a high level of uniformly distributed intensity. The Powell lenses are frequently used as laser line generators for machine vision applications.
In some instances, such a high level of uniformly distributed intensity is not required. As Powell lenses represent an expensive way to get a line pattern of more uniformly distributed intensity (i.e., the production of Powell lenses requires high-precision equipment) , the Powell lenses represent an expensive solution, especially when such a high level of uniformly distributed intensity is not required. Furthermore, Powell lenses have been limited to uses where the light source is a well collimated diffraction-limited light beam, such as a laser beam, and this further increases the cost of such line generators. Extended sources of light have not been used with Powell lenses.
It is therefore an aim of the present invention to provide a new apparatus and method for generating line patterns of light.
Therefore, in accordance with the present invention, there is provided an apparatus for generating linear patterns of light, comprising at least one light source emitting a first light beam, an anamorphic system positioned downstream of the light source and adapted to receive the first light beam of the light source for concentrating the first light beam such that the first light beam would project a first linear pattern on a far field, and at least one diffractive optical element positioned downstream of the anamorphic system for receiving and diffusing the first light beam of the anamorphic system in at least two second light beams, the two second light beams overlapping one another at least partially so as to project a second linear pattern on the far field of altered intensity with respect to the first linear pattern.
Also in accordance with the present invention, there is provided a method for generating linear patterns of light, comprising the steps of: i) emitting a first light beam; ii) collimating the first light beam in at least a longitudinal dimension; and iii) diffusing the first light beam into at least two second beams, said at least two second beams at least partially overlapping one another to project a linear pattern on a far field.
Further in accordance with the present invention, there is provided a system of apparatuses for generating linear patterns of light, comprising at least one light source emitting a light signal, at least two optical fibers each emitting a first light beam to one of the apparatuses, each apparatus comprising an anamorphic system positioned downstream of a respective one of the optical fibers and adapted to receive the first light beam of the respective one of the optical fibers for concentrating the first light beam such that the first light beam would project a first linear pattern on a far field, and at least one diffractive optical element positioned downstream of the anamorphic system for receiving and diffusing the first light beam of the anamorphic system in at least two second light beams, the two second light beams overlapping one another at least partially so as to project a second linear pattern on the far field of altered intensity with respect to the first linear pattern.